In the manufacture of glass objects, it is frequently necessary to handle or process hot products or hot semi-finished products with a temperature between 200.degree. and 1000.degree. C. The hot products or semi-finished products usually have a temperature above 200.degree. C., commonly in the range of 300.degree. to 700.degree. C., depending on the processed glass type and the respective production step. The devices in or with which this handling is performed, are mostly transporting, handling and processing machines, which include extrusion, shaping, positioning, transfer and removal machines or components of such machines, which come into contact with the hot glass object, i.e. grippers, pushers, slides, turning devices, depositing plates, slide and starter rails, slide pieces, conveyor belt segments, deflection rollers, conveyor rollers, stripper plates, push rods, deflectors, gripper claws, inserts, cooling oven push rods, supports for conveyor devices, positioning gauges, moulds or mould parts, cutters, etc.
In many cases only the actual contacting areas of the components, where a combined thermo-tribo-mechanical stress occurs, are made of temperature resistant materials, whereas the components themselves are not.
Until now mainly asbestos or asbestos containing materials were used for such hot handling applications. Due to the health hazards involved with the use of asbestos, the use of asbestos is more and more reduced and substitutes are frequently already used.
All known asbestos substitutes, however, have one or more specific disadvantages.
Commonly used ceramics fiber materials are subject to high wear and tear, i.e. they only have a limited life, which results in high retrofitting costs. They release rubbed-off fibers, which results in the contamination of machines and workshops and the possible disruption of sensors, the rubbed-off fibers additionally also absorb lubricant oil fogs from the air which, due to their large surface, leads to an increased fire hazard.
Massive, monolithic ceramics tend to get brittle fractures, particularly in the case of impact or knock stress, but also in cases of a slowly applied tension, such as during the application of screw connections, and it only possesses a low thermo shock resistance and is difficult to join, for instance in screw-connections with machine parts of steel.
Graphite is subject to high wear and tear, which results in high retrofitting costs, also tends to get brittle fractures if subjected to impact or knock stress, is also difficult to join, possesses a high heat conductivity, which easily results in material cracks during hot glass handling and tends to oxidize in a hot oxidizing atmosphere. Graphite is frequently also too smooth in order to grip hot glass.
Metals and anodizations frequently possess a high specific weight, which results in an increased energy consumption, especially with high cycle frequencies (accelerations), they possess a high heat conductivity, which easily results in material cracks, and they can result in rubbed-off metal parts, which immediately results in waste during the production or indirectly results in waste since metal traces in hot glass induce cracks.
Plastics, e.g. those on a fluorocarbon resin or polyimide basis only possess an insufficient thermic stability, they deform uncontrollably if the thermic stress is too high, and can additionally release aggressive or health hazardous gases which contaminate the glass products. A possible result of the contamination is that the glass products cannot be imprinted any more.
Metals and ceramics furthermore possess very high coefficients of friction in contact with hot glass, so that it is frequently necessary to apply large quantities of lubricating oils or firm lubricants. These lubricants spread throughout the plant, through evaporation, for instance, and have to be regularly removed in a labor-intensive process, in order to minimize the danger of accidents through slipping on floor and stairs.